When the two cars collided that February night, the impact spun around the Volkswagen Passat and smashed it into a bridge support under the freeway. After the screeching and the thud, the shocking groan of metal hitting metal and then concrete, the only sound in the cold night was the insistent revving of the Passat's engine.

Chris Williams once worked as a hospital orderly, so he immediately could see his future. In the back seat were the deep, bloodless gashes in 11-year-old Ben's face, and the motionless body of 9-year-old Anna. As he watched, his pregnant wife Michelle gave her last, sad exhale. Williams himself was in so much pain it was a struggle to turn the key in the ignition. In the minutes before the ambulances arrived, as horrified passers-by tried to extricate him, Williams put his head back and moaned.

But then a thought rose to the surface: "Whoever has done this to us, I forgive them. I don't care what the circumstances were, I forgive them."

Later, police found a dazed 17-year-old boy several blocks from the scene. Police estimate Cameron White had been going at least 60 mph and was high on vodka when his car came down the hill on 2000 East, heading straight for the Williams family car, killing Williams' wife, two of his children and severely injuring a third. Still, despite the realization that his loss involved not an accident but someone's bad choice, Williams held fast to his decision to forgive.

Like all examples of extravagant forgiveness, that decision was both a simple resolution and an epic, complicated journey  one that confounds those of us who imagine how vengeful we might feel in the face of such a horrific loss.

Williams made headlines last February when he publicly forgave White. That was just six weeks after another grieving father, Gary Ceran, publicly forgave the drunken man who killed his wife and two of his children in a Taylorsville intersection on Christmas Eve 2006.

In March, another grieving parent, Anna Kei'aho, stunned a courtroom full of onlookers when she forgave the man who had gunned down her son. In October, Ben Howard stood up in a Layton courtroom and requested leniency for the driver who slammed into his van on Highway 89, killing his wife and two of his children, a request that made the judge and court bailiff cry.

The fact that these acts of forgiveness surprise us is a reminder of how difficult an act it is. In a world where old grudges erupt daily in roadside bombs, to forgive may or may not be divine, but it isn't always human nature either.

The forms of forgiveness

Years earlier, when Chris Williams was 16, a little boy had run out onto 8th Avenue and into the path of his car. And so, the night half his family died, after White was apprehended, Williams remembered what it was like to be a teenager all alone in the back of a police car. But his desire to forgive had less to do with his own experience as a teenager who had killed a child, he says, and more to do with what by then had become a kind of practice.

"It was almost like I had drilled myself for that moment," he says.

Williams had essentially trained  in the way a marathon runner might start with leg exercises and shorter runs  so that when the time came to forgive the nearly unforgivable, he was ready.

Part of that training included a prayer he used to say after his first son, Michael, was born: "Help me appreciate him, and if he's taken prematurely, give me strength." Three years ago, when Michael nearly died of toxic shock syndrome, Williams said the same prayer.

The point, he says, is that none of us is entitled to a perfect life. Really understanding that, he says, is central to being able to forgive. To think that things will always work out in our favor, he says, is to set ourselves up for anger, at other people and at God.

And yet this is how most of us move through our days: expecting that we deserve a good life, desperately hoping that we can hold on forever to everything that is good. These are what forgiveness researcher Fred Luskin, co-founder and director of the Stanford University Forgiveness project, calls "unenforceable rules."

And, too, humans are hard-wired to want payback. Studies done in Switzerland, using fMRIs (functional magnetic resonance imaging) on people confronted with a simulated grievance show that the brain's pleasure pathways light up right before a person enacts vengeance, says professor Everett Worthington Jr. of Virginia Commonwealth University, who researches forgiveness and is a clinical psychologist.

To forgive goes against "the natural impulse to make things even," Worthington says.

There are now scores of people researching forgiveness, producing 950 studies as of 2005, up eightfold from eight years earlier. Before Dr. Robert Enright of the University of Wisconsin launched the field 20 years ago, though, the concept of forgiveness was considered the domain of religion, a topic for the pulpit but not for academic study or even psychotherapy. Then researchers showed that the inability to forgive has an impact on health  on blood pressure, immune response and depression, for example  and people started paying attention.

There are two kinds of forgiveness, says Worthington: decisional and emotional. So a person may choose to forgive another person, but if he's still feeling bitter, it hasn't been an emotional forgiveness. Follow-up studies of the Amish parents who immediately forgave the man who shot 10 schoolgirls in October 2006 show that "they still express difficulty dealing with the losses emotionally," says Worthington.

That's not to say that a person whose daughter was gunned down wouldn't still feel immensely sad a year later. But, Worthington explains, "if I'm sad because of a loss, that's grief. If I feel resentful and angry, that's emotional unforgiveness."

There are personality characteristics that tend to make a person more or less forgiving, Worthington says. People who are more "agreeable" are more likely to forgive; people high in "neuroticism" (not the tendency to be neurotic but the tendency to react hyper-emotionally to stimuli) tend to form grudges more easily. Anger, anxiety, fear and a narcissistic sense of entitlement also contribute to a person's inability to forgive, as does a person's tendency to ruminate.

"Rumination is what gets people in trouble when they have been wronged," he says.

Containing grievances

Think of your brain as a house, with rooms you rent out, says Stanford University's Luskin in his book "Forgive for Good."

"We can rent our grievances the master bedroom and build them a hot tub out back. ... We can allow them to put their stuff in all the rooms of the house, or we can restrict them to a small room in the back." In other words, Luskin writes, we need to ask, "How much time do we spend thinking about our hurts and disappointments? And, when we think about them, how much intensity is there?"

If he could tell people anything, Chris Williams says, it would be this: "Forgive for your sake, not the other person's." Forgive because, if you don't, your bitterness will consume you. Or, as Luskin writes, "Besides the anger and hurt, the loss of joy, love and intimacy mar the lives of those who do not forgive."

"He could be a shadow," Williams says about the teenager who killed his wife and children. "He could be rocks in a backpack I'd be carrying everywhere."

On the other hand, to forgive doesn't necessarily mean to invite the teenager into his life, Williams says. "This is the box you're going to live in," he tells the idea of White. "You're contained." If he focuses on the fact that White hurt his family, that's letting the teenager out of the box, Williams says. That's why he didn't attend White's parole hearing. "The box is now incredibly small."

To reconcile with the person who wronged you  getting to know him if he's a stranger, becoming friends again if he's someone you know  may be advisable in situations like post-apartheid South Africa, where it's important to build community. But it's not always necessary, or advisable. Researchers say that people who have been sexually abused might be more harmed than helped by being encouraged to talk to their abusers.

But there are also stories of people who have reached out to, and even become friends with, the people who hurt them. Occasionally this has resulted in a collaboration to fight drunken driving or violence or war. You can find some of these stories at www.theforgivenessproject.com, a London-based organization begun by journalist Marina Cantacuzino.

Cantacuzino began her project as an exhibition called "The F Word," a nod to how complicated the notion of forgiveness is. "For some people," writes Cantacuzino, "forgiveness is a very dirty word indeed."

Forgiveness as a skill

Here's what forgiveness is not, says Stanford's Luskin: forgetting that something painful happened, minimizing your hurt, not holding people accountable for their actions. Here is what forgiveness is: a choice, "the practice of extending your moments of peacefulness," something completely under your control.

Forgiveness may not be our first impulse, but it's a teachable skill, Luskin says. "You can set up classes and teach people to forgive, in the same way you can set up classes to teach people how to play the piano."

He has taught forgiveness to mothers in Northern Ireland whose children died in sectarian violence, and to Americans with long lists of grievances: spouses who have been cheated on, grown-ups who had been abandoned as children, business people whose partners lied to them. Now, as detailed in his new book, "Forgive for Love," Luskin is working with couples, using forgiveness as a relationship tool.

Forgiveness, he says, doesn't depend on the intensity of the wrong done to you, nor does it require that the other person repent or ask for your forgiveness first.

"People languishing in a hell of their own making because they simply can't let it go," is the way Ron Yengich describes the people who don't forgive. In his years as a defense attorney, Yengich has seen a few stunning examples of people who have forgiven his clients, most recently the courtroom statement of Anna Kei'aho, the mother who told a 3rd District judge that she and her family extend their love to her son's killer and his family. More often, though, Yengich has seen a parade of people who choose to hold onto their anger and hurt.

Society isn't always very helpful, Yengich says. "What we teach in America is: Once you've been victimized, maintain your victimhood forever, at all costs, and use that as an excuse for whatever happens to you in the future." As for our feelings about perpetrators, he says, "our idea of justice is fairly simple: once we've got our foot on someone's neck, justice for us is to press down as hard and as long as we can."

Punishment is one thing, a necessary part of the legal system, the part that looks for justice. But revenge is something else, says Yengich, who understands the impulse. Forty years ago, when he heard that Robert Kennedy had been shot, Yengich realized that he'd like to "rip Sirhan Sirhan to shreds." That vengeful person still exists in him, he says. "That's one of the things I have to worry about every day. That's the guy I'm working on."

Like Chris Williams and researcher Everett Worthington, Yengich looks for help from religion and philosophy. "Not to sound too weird on this stuff," he says, "but one of the problems we have in our society today is we believe we can do all this on our own."

Worthington says studies have shown that people who have a religious or philosophical viewpoint that values forgiveness are more willing to grant forgiveness for being wronged. "Whereas if they were raised in an environment where they never consider forgiveness an option, it's more difficult to head down that path."

Humans are hardwired for justice, he says, "but mercy and love have to percolate." Worthington himself had a chance to understand this in a less academic way in 1995, when his own elderly mother was killed by two men with a crowbar during a New Year's Eve burglary. At first he wanted to take a baseball bat to the murderer and "beat his brains out." It was only later that he was able to forgive.

In Islam, explains imam Shuaib-ud Din of Utah Islamic Center, the relatives of a murder victim can advise the court to forgive the murderer  and no punishment will be carried out. But it's not "turn the other cheek," says Din. "Every person who has been wronged has the right to seek recompense. On the other hand, because Islam is a balanced religion, it also encourages us to forgive."

As a Jew, says orthodox Rabbi Benny Zippel of Chabad Lubavitch in Salt Lake City, every night before he goes to bed he recites the "shema": "I forgive all the people who have wronged me in the past day." It's a practice  "so if you're ever faced with the big task of having to forgive someone of a major transgression, it shouldn't be a concept that's totally foreign to you."

And then, says James Wakefield of Salt Lake Theological Seminary, perhaps we can take one more difficult step: not just to forgo the retaliation we're entitled to but "to pray for the blessings of the one who injured me ... to think through their need for grace, their brokenness, my own propensity to sin, our common humanity."

Forgiveness as a choice

In the months before the accident, Chris Williams began rereading the Gospels of the New Testament, as the leaders of the LDS Church had encouraged members to do. Williams was a busy man, lay bishop of his neighborhood ward and a technical sales manager for IBM, so sometimes he just listened to the Gospels on his tape recorder as he rode the chairlift on ski outings with his children.

Although he had read the story of the Prodigal Son before, this time around he was touched by one image: an elderly father running toward a wayward son, arms outstretched in love.

One Sunday evening last month, Williams stood in front of a packed wardhouse in West Jordan and talked about what that story has come to mean to him: "If my Heavenly Father can treat me this way, if when we approach him he runs to us, then who am I to hold a grudge, to judge another person, to not forgive?"

It was one more piece of healing in a year of forgiveness, a year in which Rwandan native Louis Gakumba stood on the stage at the Rose Wagner theater and told the story of a woman in his country whose children and husband were butchered by Hutus. The woman, Gakumba explained, has chosen not only to forgive the killer but to take him in as a son. A few months earlier, a fictional character in the chilling play "Frozen" had stood on a different stage at Rose Wagner and forgiven the man who had murdered her daughter.

As a species we hold grudges and blow each other up for every past offense we can't let go of. But occasionally, even though his friends try to get him to move toward anger, a man will choose to forgive. And then another man. A woman will reach out to the family of the man who killed her son.

After he publicly forgave Cameron White, Williams received over 800 e-mails. Some were messages of condolence. But many were vows to let go of anger and resentment. "If you can forgive," they said, "I can too."